1. Field of the Invention
The present invention relates to a light collector adaptable for use with a generally planar photodetector to provide a uniform photodetector output response over a predetermined polar angle range regardless of the polar angle of incidence of light upon the collector.
2. Description of the Prior Art
Personal sun exposure measurement devices, or so-called UV personal dosimeters, utilize a planar photodetector which generates an output response signal in accordance with the magnitude of the radiation incident thereon. Since the output response signal of the photodetector varies as a function of the angle of incidence of the illuminating light, these devices will not provide the desired measurement accuracy unless they are properly oriented with respect to the source of the incident radiation. Thus it is necessary to provide a suitable aiming mechanism which maintains the photodetector in the most optimal relationship with respect to the sun to insure that the maximum intensity of the UV-radiation is detected. The aiming mechanism may take a variety of forms.
U.S. Pat. No. 5,036,311 (Moran et al.) exemplifies a UV dosimeter that measures incident solar UV radiation in a weighted manner corresponding to the erythemal action spectrum of human skin. The dosimeter of the Moran patent includes an analog indicator that permits a user to align the photodetector to the sun so that the angle of incident radiation lies within the broad range (approximately plus/minus forty five degrees) over which the dosimeter is accurate. The dosimeter device disclosed in U.S. Pat. No. 5,008,548 (Gat), which is in a form similar to a pocketwatch, includes an accessory stand for properly orienting the dosimeter with respect to the incident radiation. The dosimeter disclosed in U.S. Pat. No. 4,985,632 (Bianco et al.) takes the form of a wristwatch designed to be worn by the user.
However, when such devices are properly positioned to receive direct solar radiation they will typically not be positioned to detect radiation that is reflected or scattered from snow, water or soil surfaces, as might be experienced by a person when skiing, swimming, boating or reclining on a sandy beach.
It is, therefore, believed advantageous to provide a light collector for use with a photodetector that provides a uniform output response from the photodetector over a range of polar incidence angles exceeding 180 degrees. More preferably, it is believed advantageous to provide a light collector that provides a uniform output response from the photodetector over a polar angular range of at least two hundred seventy degrees.
Other radiation measurement devices are known to the art.
U.S. Pat. No. 4,178,101 (Booth) and U.S. Pat. No. 4,804,849 (Booth et al.) both disclose a spherical collector with an outer translucent surface. A light pipe extends from the center of the sphere to transmit collected light to a remotely located photodetector. Each reference also discloses a filter assembly between the end of the light pipe and the photodetector to achieve the desired spectral response.
U.S. Pat. No. 3,180,210 (Tyler) also discloses a hollow spherical collector with an outer translucent surface. The sphere has an opening therein through which collected light exits the sphere via a tubular extension and is-transmitted to a remotely located photodetector.
The article by W. S. Maddux, "A 4- Light Meter", Limnology and Oceanography, 1966, 2, 136-37, shows an elongated photodetector assembly positioned at the center of a solid sphere of a light scattering plastic foam material (polystyrene).
The article by Sasaki et al., "A 4- Underwater Irradiance Meter", Journal of the Oceanographical Society of Japan, Volume 22, Number 4, August 1962, discloses a pair of photodetectors, each with an opal window of hemispherical form, that imparts a polar angular response that is improved over that of a photodetector having a planar opal window.
The article by Rich and Wetsel, "A Simple Sensitive Underwater Photometer" Limnology and Oceanography, 1969, 14, 611-13, shows the use of a hemispherically-shaped foam member as a light scattering element in combination with a planar opal glass light scattering element disposed immediately in front of a photocell.
SPSE Handbook of Photographic Science and Engineering, Woodlief Thomas, Jr., Editor, published by John Wiley and Sons (1973), at pages 856-57 discloses a densitometer using an integrating sphere. Pages 1142-43 of the same text shows a light meter having a hemispherical translucent dome.